[postgis-users] Spatial Analysis? (PostGIS -> Well-Known Text -> JTS)

[Obe, Regina DND\MIS]

I'm not sure if there has been a recent version of pgsql2shp that can take
ad hoc queries.  I remember there was some discussion of it, but haven't
attempted that.

Normally what I do is use the option 2 you proposed  - whereby I create a
view and then use pgsql2shp to dump it out as a shapefile.  That works
pretty well.

-----Original Message-----
From: C F [mailto:gis_consultant at hotmail.com]
Sent: Tuesday, May 21, 2002 12:01 PM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] Spatial Analysis? (PostGIS -> Well-Known Text
-> JTS)


Hello,
I'm just starting to look into PostGIS (don't even have it installed yet) 
and had a few questions about it if somebody wouldn't mind taking a stab at.

  First I'll tell you the requirement I'm after, then give you my ideas.  
What I would want is to be able to "cookie cut" (intersect) points, lines, 
and polygons from PostGIS layers using a polygon shape and put the results 
into a shapefile.  For now, I *might* be satisfied with only being able to 
do a bounding rectangle intersection since I see that sort of spatial 
operation is currently available in PostGIS.

1)  It looks like the pgsql2shp utility only takes the entire layer, you 
cannot tell it to extract certain extents. Correct?

2)  I assume that you can create views of your spatial data in 
PostGIS/PostgreSQL.... if so, would a workaround for #1 be to create a view 
using one of the spatial operators (something like ~=) and then use 
pgsql2shp on that view (if it works on views)?

3)  If #1 and #2 are not good how about doing a query and putting it out to 
well-known text and then using some other product to convert that to a 
shapefile?  The problem is, I'm not seeing much available in that 
department.  It looks like OGR could do it... has anyone done this?

4)  Now... if I really wanted to intersect layers with a non-rectangular 
polygon, what about using JTS?  PostGIS can output features in well-known 
text and JTS can read in well-known text... and it has the ability to do 
spatial operations.  I'm sure you can see where I'm going with this... 
PostGIS -> Well-Known Text -> JTS -> Well-Known Text -> Shapefile
Sounds extremely ugly and slow, but I'm curious if anyone has attempted it 
(I don't think JTS can do Well-Known Binary).

Any comments would be much appreciated!  Thanks.

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